1. Field of the Invention
The present invention is related to methods of impairing progenitor hematologic cancer cells or treating hematologic cancer by targeting a cell surface marker specific for progenitor hematologic cancer cells. The present invention is also related to a method for diagnosing hematologic cancer.
2. Background of the Invention
Stem cells are commonly found in a variety of mammalian tissue systems. While the criteria by which such cells are defined vary depending upon the specific context, two properties are generally regarded as central features of stem cell populations: (1) stem cells must exhibit some capacity for self-replication or self-renewal, and (2) stem cells must be capable of differentiating into appropriate lineages (Potten C S: Stem Cells. London, Academic Press, 1997). Cells of this nature have been described for a number of tissues including hematopoietic, embryonic, neural, muscle and hepatic systems (Lemischka I R. Clonal, in vivo behavior of the totipotent hematopoietic stem cell. Semin Immunol 1991, 3: 349-55; Morrison S J, et al., The biology of hematopoietic stem cells. Annu. Rev. Cell Dev. Biol. 1995, 11: 35-71; Robertson E J., Using embryonic stem cells to introduce mutations into the mouse germ line. Biol Reprod 1991, 44: 238-45; Gage F H., Mammalian neural stem cells. Science 2000, 287: 1433-8; and, Alison M, et al., Hepatic stem cells. J Hepatol 1998, 29: 676-82). Thus, it is perhaps not surprising that similar cells have recently been documented in the context of malignant populations (Bonnet D, et al., Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell. Nat. Med. 1997, 3: 730-737; Blair A, et al., Most acute myeloid leukemia progenitor cells with long-term proliferative ability in vitro and in vivo have the phenotype CD34(+)/CD71(xe2x88x92)/HLA-DR-. Blood 1998, 92: 4325-35; Cobaleda C, et al., A primitive hematopoietic cell is the target for the leukemic transformation in human Philadelphia-positive acute lymphoblastic leukemia. Blood 2000, 95: 1007-13). Indeed, a stem cell is in some respects the ideal target for malignant transformation in that relatively little biological change is required. Since stem cells already possess the genetic programming necessary to be highly proliferative and developmentally plastic, one can imagine that relatively subtle perturbations might be sufficient to induce disease.
One example of neoplasia arising from malignant stem cells has recently been documented in the hematopoietic system in the case of acute myelogenous leukemia (AML). This disease is characterized by premature arrest of myeloid development and the subsequent accumulation of large numbers of non-functional leukemic blasts. While leukemic blast cells are often of clonal origin and display relatively homogeneous features, it has been demonstrated that such populations are organized in a hierarchical fashion, analogous to normal hematopoietic progenitors. Thus, there is a phenotypically defined leukemic stem cell population that is sufficient to propagate leukemic blasts both in vitro and in vivo in xenogeneic mouse models of human AML (Bonnet D, et al., Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell. Nat. Med. 1997, 3: 730-737; Blair A, et al., Most acute myeloid leukemia progenitor cells with long-term proliferative ability in vitro and in vivo have the phenotype CD34(+)/CD71(xe2x88x92)/HLA-DR-. Blood 1998, 92: 4325-35; Cobaleda C, et al., A primitive hematopoietic cell is the target for the leukemic transformation in human Philadelphia-positive acute lymphoblastic leukemia. Blood 2000, 95: 1007-13; Blair A, et al. Lack of expression of Thy-1 (CD90) on acute myeloid leukemia cells with long-term proliferative ability in vitro and in vivo. Blood 1997, 89: 3104-12). The concept of a leukemic stem cell (LSC) becomes critically important in considering the etiology of human disease. Clearly, in order to achieve durable remission, it will be necessary to specifically ablate the primitive or progenitor LSC population. However, previous studies (Terpstra W, et al., Fluorouracil selectively spares acute myeloid leukemia cells with long-term growth abilities in immunodeficient mice and in culture. Blood 1996, 88: 1944-50), as well as data from our group, suggest that LSC""s are biologically distinct from more mature leukemic blasts and may not be responsive to conventional chemotherapeutic regimens. This observation is consistent with the clinical profile frequently seen for AML, wherein a majority of patients can achieve apparent complete remission, but in most cases will relapse (Schiller G J., Treatment of resistant disease. Leukemia 1998, 12 Suppl 1: S20-4; Paietta E., Classical multidrug resistance in acute myeloid leukemia. Med Oncol 1997, 14: 53-60). If LSC""s are more refractile to chemotherapy than blasts, it is attractive to propose that surviving stem cells are a major contributing factor to leukemic relapse. Thus, strategies that specifically target progenitor leukemia cells may provide more effective treatment for leukemia patients. In 1997, Bonnet and Dick described the phenotype for LSC""s as CD34+/CD38xe2x88x92 (Bonnet D, et al., Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell. Nat. Med. 1997, 3: 730-737). We report that the IL-3 receptor alpha chain (CD123) is highly expressed on leukemic but not normal CD34+/CD38xe2x88x92 hematopoietic cells. In view of this state of the art, there is a need in the art to provide a diagnostic method for detecting leukemia at an early stage, as well as more effective methods of treating this disease.
The present invention relates to a method of using compounds that bind to the human CD123 molecule (CD123 ectopeptide), in the diagnosis and treatment of hematologic cancers (e.g., leukemias and malignant lymphoproliferative disorders). The CD123 specific compounds and mimetics have particular utility as pharmaceuticals and reagents for the therapy of hematologic cancer or malignant disease states and for the diagnosis of hematologic cancer disease states. In one embodiment, the present invention provides a method of impairing a hematologic cancer progenitor cell comprising contacting the cell with a compound that selectively binds to CD123 in an amount effective to impair the progenitor hematologic cancer cell. This contacting step may occur in various environments, including in vitro and in vivo in the body of an animal, including a human.
Throughout this application, reference will be made specifically to leukemia in describing certain embodiments of the present invention. However, it is understood that the present invention is not limited to diagnosis and treatment of leukemia or malignant lymphoproliferative disorders alone, but to any disease in which the cancerous cells selectively express CD123, which includes the genus of hematologic cancer.
In one embodiment, the present invention is directed to a method of detecting the presence of CD123 on, for example, a leukemia progenitor cell. Thus, the invention is also directed to a method of diagnosing leukemia. It is understood that by using a labeled ligand to bind to CD123, it is possible to detect the presence of leukemia progenitor cells. Thus, it is also possible to diagnose the likelihood of the onset of leukemia in patients possessing such leukemic progenitor cells expressing CD123. The CD123 binding ligand may be an antibody to CD123, or it may be any of a variety of molecules that specifically bind to CD123. Furthermore, the label can be chosen from any of a variety of molecules, including, but not limited to, enzymatic compounds, or non-enzymatic compounds that serve as a reporter of the presence of the ligand which has bound to the CD123 molecule. Examples of such labels include those that are, for example, radioactive, fluorescent, chemiluminescent or absorbant-based, or a combination of the foregoing. In one embodiment, an assay is provided for detecting the presence of progenitor leukemia cells in a sample by detecting the presence of CD123 in the sample, which may be accomplished by introducing a compound that selectively binds to CD123 and determining whether the compound binds to a component of the sample.
In another series of embodiments, the present invention also provides compounds or molecules which mimic (mimetics) the three-dimensional structure of part or all of the compounds such as peptides, antibodies, carbohydrates, lipids or nucleic acids that bind to CD123, and in the case of antibodies, of the binding pockets of the antibodies, or of the complementarity determining regions (CDR""s).
The present invention also provides pharmaceutical preparations comprising a pharmaceutically acceptable carrier; and any one or more of the CD123 specific compounds and mimetics described above.
In another set of embodiments, the present invention provides a method for the treatment of leukemia, comprising administering to a human subject or other animal in need of such treatment a therapeutically effective amount of the compounds or their mimetic pharmaceutical compositions described above.
In still another set of embodiments, the present invention provides a method of selectively purging leukemic stem cells from bone marrow. These stems cells may give rise to leukemia progenitor cells, or they may be the progenitor cells, which may be impaired by the method of the invention using various compounds or their mimetics and cytotoxic agents that may be contacted to either a bone marrow sample or injected into a bone marrow of an individual, thereby destroying at least some of the leukemic stem cells in the bone marrow.